1. Field of the Invention
This invention is related to U.S. patent application Ser. No. 581,359 filed Feb. 17, 1984 and concerns a molten metal discharging device adapted to be mounted at a bottom portion of a container such as a ladle or tundish for use in the casting of molten metal or the like.
2. Discussion of the Background
In the case of casting molten steels, for instance, by way of a conventional continuous casting process, a molten metal discharging device comprising a stationary plate and a slide plate is attached to the bottom portion of a ladle or tundish accomodating the molten steel and the flow rate of the molten steel is adjusted by causing the slide plate to move slidably with respect to the stationary plate thereby opening or closing a passage bore, in the stationary plate, for the molten steel. In the above-mentioned molten metal discharging device, an inert gas such as argon is introduced from the stationary plate into the molten steel so as to prevent the clogging in the passage bore caused by the solidification of the molten steels and/or deposition of oxides of metal or metalloid such as Al, Ti, Ca, Cr, Mn, Si or Ni.
Such type of the conventional molten metal discharging device is shown in FIG. 1.
In FIG. 1, an upper nozzle 1 having a molten metal passage bore 1a is secured to a bottom portion of a tundish (not illustrated). Below the upper nozzle 1, is attached a molten metal discharging device 14 comprising an upper stationary plate 2, a slide plate 3 and a lower stationary plate 4 having molten metal passage bores 2a, 3a, 4a respectively. The slide plate 3 is moved slidably between the upper stationary plate 2 and the lower stationary plate 4 in the direction of A or B to open or close the passage bores 2a, 3a, 4a thereby adjusting the flow rate of the molten steel and completely closing the passage bores 2a, 3a, 4a. The main body 2b of the upper stationary plate 2 is made of dense refractory material and an annular gas supply member 5 made of porous refractory material is tightly fitted over the entire circumference of the upper and enlarged inner circumferential wall surface 2c of the main body 2b. A gas pressure-uniformalizing zone 6 in the form of an annular space is defined between the annular porous refractory member 5 and the main body 2b of the upper stationary plate 2. Further, a gas introduction hole 7 communicated with the gas pressure-uniformalizing zone 6 is formed in the upper stationary plate 2, and a gas introduction pipe (not shown) is connected to the gas introduction hole 7. A submerged nozzle 8 is attached at the bottom of the lower stationary plate 4 and inserted at the lower end thereof into a mold 9.
In the illustrated conventional device 14, molten steels poured from the tundish (not illustrated) is supplied to the mold 9 through the passage bores 1a, 2a, 3a, 4a and 8a respectively formed in the upper nozzle 1, the upper stationary plate 2, the slide plate 3, the lower stationary plate 4 and the submerged nozzle 8 and then cooled within and below the mold 9. As the result, a molten layer 10, a partially-molten layer 11 and a solidified layer 12 are formed within and after or below the mold 9. Numeral 13 represents a mold powder layer 13 disposed above the molten layer 10.
In the molten metal discharging device 14 as described above, a gas is introduced from the gas introduction hole 7 into the molten steel through the gas supply member 5 to agitate the molten steel when the molten steels are started to be poured from the ladle to the tundish, thereby preventing the solidification of the molten steel within the passage bore 2a in the upper stationary plate 2 and facilitating the initial opening of the bore 2a. Further, the gas is introduced through the porous gas supply member 5 to agitate the molten steel also during casting for preventing the solidification of the molten steel and/or deposition of metal oxides to thereby prevent the clogging in the bore 2a, etc. Furthermore, supply of the gas serves to float up the oxides or impurities in the molten steel to reduce the content of the oxides or impurities incorporated in the steels to 1/5-1/10 as compared with those steel products obtained without such gas supply.
However, the foregoing conventional molten metal discharging device 14 has the drawbacks due to the use of the gas supply member 5 made of porous refractory material for the supply of the gas into the molten steel as described below:
(a) Since the sizes of the gas bubbles introduced into the molten steel are relatively small, agitating effects by the gas bubbles are relatively low, therefore a reliable prevention of the clogging in the passage bore 2a, etc. cannot always be expected.
(b) The gas introduction member is inferior in the corrosion-resistance due to its porous texture.
This invention has been accomplished in view of the above and the object thereof is to provide a molten metal discharging device at least capable of minimizing the foregoing problems, that is, a molten metal discharging device having less fear that the molten metal passage bore may be blocked by the solidification of molten metal and/or deposition of metal oxides, and having an improved corrosion-resistance to the molten metal.